CHAPTER VI 



The Ribbon Worms 



{Phylum Neinertea) 



Th 



.HE smallest of these soft, elongated, mostly ma- 

 rine worms may be threadlike and only a fraction of 

 an inch long. The giants of the group, however, are 

 the longest, though certainly not among the largest, 

 of invertebrates. Exactly how long it is difficult to say, 

 for all the ribbon worms are highly elastic, and the 

 really long ones stretch out, threadlike, for yards 

 and yards — some say much more than 30 yards in 

 Linens longissUniis, the blackish brown worm of the 

 North Sea. The English call it the "bootlace worm." 

 Modest length, not more than about 8 inches, is more 

 usual. The body may be cylindrical, as in Linens. 

 though more often flattened on both sides or flattened 

 below and convex above. 



Bright colorings of orange, red, purple, or green, 

 these mostly on the upper surfaces, may betray the 

 worms to the eyes of naturalists scanning rocky crev- 

 ices or overturned stones at low tide. More often the 

 colors blend with red or green algae or other colorful 

 growths among which the worms live. To find small 

 nemerteans. collectors place masses of seaweed or of 

 bryozoan colonies that resemble delicate seaweed in 

 dishes of sea water and let the small worms creep 

 out on the walls of the dishes, where they can easily 

 be seen. Some worms are white or yellowish, others 

 somber grays or browns, but many are handsomely 

 patterned with strongly contrasting rings or longitu- 

 dinal stripes or both. The front end is not set off as 



a distinct head, though the tip may be expanded and 

 have colored markings, several or numerous eyes, 

 and sensory grooves, which make it look superfi- 

 cially like a head. The rear end is more or less 

 pointed. 



Another common name, proboscis worm, less 

 widely used, calls attention to the most distinctive 

 feature of nemerteans. This is a long, extensible, tu- 

 bular proboscis that can be shot out the front end 

 with explosive force to grasp prey or discourage ene- 

 mies. The proboscis coils about the prey, holding it 

 firmly and entangling it in sticky mucus which may 

 be irritating or even poisonous. The proboscis is also 

 everted as a device for burrowing in sand or mud or 

 for attaching to objects as an aid in creeping about. 

 It can be made to evert by irritating the animal, by 

 plunging it into fresh water, or by placing it in a small 

 dish of sea water and cautiously adding alcohol, drop 

 by drop. The accurate aim of the proboscis receives 

 recognition in the technical name of the phylum, 

 Nemertea, from a Greek word that means "unerr- 

 ing." In some of the commonest worms the tip of the 

 proboscis is armed with a sharp spike or stylet, which 

 pierces the prey, sometimes several times, before a 

 toxic secretion is poured on. Worms may have two 

 or more pouches with a reserve supply of stylets, so 

 that replacement can be made quickly if the main 

 one is damaged. When not in use the proboscis is 



[129 



